The present invention relates generally to high pressure flow valves and, more particularly to flow control valves for use in fluid systems, both gas and liquid, to channel fluids at desired flow rates and pressures. Ideally, a control valve opens when compelled to do so, by means of an external force, such as an air hydraulic operator or a threaded stem to raise or lower the stem or to close or open the valve. This ideal valve permits passage of a particular volume of fluid necessary to maintain the predetermined flow system parameters and then close tightly, and instantly, with zero leakage at a pre-set command. Unfortunately, in actual practice, this ideal is not always realized.
Commonly used control valves have a cracking or threshold pressure level, the pressure at which the valve begins to open, and a full flow pressure level, the pressure required to open them fully. The difference between full-flow pressure and cracking pressure levels is the pressure differential of the valve, commonly referred to as the valve override. The smaller the pressure differential, or override, the greater the sensitivity of the valve.
Prior control valves generally exhibit excessive differential which causes them to open at the cracking threshold at a pressure level far below the pre-set maximum system pressure level, which, greatly diminishes the useful flow in the fluid system.
Prior valves are also prone to excessive chattering which is generally caused by an instability of the internal fluid sealing elements. In addition, these prior devices also exhibit an objectionable characteristic referred to as "dead band" where the valve closes at a pressure value which is different than the pressure at which the valve opens.
Ideally, a control valve of this type should exhibit a zero dead band characteristic and, thus, open and close at substantially the same fluid pressure. In addition, many prior valves also develop leakage problems, particularly, in high pressure systems. For example, at 20,000 PSI and above.
Applicant is aware of the following U.S. Patents:
______________________________________ 3,181,560 to Worden et al. 4,928,920 to Feild 3,926,208 to Hoffman et al. 5,010,923 to Kouda et al. 4,311,297 to Barrington 5,046,530 to Gossner et al. 4,500,069 to Barber et al. 5,072,749 to Ligh 4,553,735 to Brundage 5,099,882 to Smith, III 4,766,932 to Heymann et al. 5,133,386 to Magee 4,832,312 to Linder et al. 5,172,886 to Takotani et al ______________________________________